The present invention relates to a rotary connector which is assembled in a steering system of a vehicle and used as electric connecting means of an air bag system or the like. More particularly, the invention relates to a rotary connector in which a flat cable is wound in the opposite direction via a reversing part in an annular space defined between a pair of housings.
In a rotary connector, a movable housing is rotatably connected to a fixed housing and a flat cable is housed and wound in an annular space defined between the housings. The rotary connector is used as electric connecting means of an air bag inflator or the like attached to a steering wheel having a limited number of rotation. The flat cable has a band-shaped member holding a conductor on a base film. Two types of a flat cable wound like a spiral and a flat cable reversely wound halfway are known. The required length of a flat cable of the latter reverse type can be made much shorter.
In the rotary connector of the reverse type, usually one flat cable is used. When the number of conductors increases as the number of circuits increases, the flat cable is widened in accordance with the number of conductors, so that reduction in the thickness of the whole rotary connector is disturbed. On the contrary, according to the rotary connector disclosed in the specification of U.S. Pat. No. 3,763,455, the conductors are apportioned to two flat cables, thereby dealing with the increase in the number of circuits.
FIG. 4 is a plan view showing a schematic construction of the rotary connector disclosed in the above specification of the patent. As shown in the diagram, a movable housing 101 having an inner cylindrical wall is rotatably attached to a fixed housing 100 having an outer cylindrical wall. A first flat cable 103 and a second flat cable 104 are housed in an annular space 102 defined between the fixed housing 100 and the movable housing 101. The flat cables 103 and 104 are housed in the space 102 on the outer cylindrical wall of the fixed housing 100 and on the inner cylindrical wall of the movable housing 101 so as to be wound in different directions. At the positions where the winding directions are reversed, U-letter shaped reverse parts 103a and 104a are formed. Inner ends of the flat cables 103 and 104 are connected to cable leading parts 107 and 108 which are arranged close to each other on the inner cylindrical wall of the movable housing 101 and are led to the outside of the movable housing 101 via the cable leading parts 107 and 108. On the other hand, the outer ends of the flat cables 103 and 104 are connected to cable leading parts 109 and 110 which are arranged close to each other on the outer cylindrical wall of the fixed housing 100 and are led to the outside of the fixed housing 100 via the cable leading parts 109 and 110. Further, groups 105 and 106 of a plurality of rollers are arranged in the radial direction in the space 102. The reverse part 103a of the first flat cable 103 is looped about one of the group 105 of rollers. The reverse part 104a of the second flat cable 104 is looped about one of the other group 106 of rollers.
In the rotary connector having the above construction, for example, when the movable housing 101 is rotated in the clockwise direction of FIG. 4, the reverse parts 103a and 104a of the flat cables 103 and 104 move in the clockwise direction in the space 102 by a rotation amount smaller than that of the movable housing 101. The flat cables 103 and 104 are in the winding state where the winding amount on the inner cylindrical wall of the movable housing 101 is larger. On the contrary, when the movable housing 101 is rotated in the counterclockwise direction, the reverse parts 103a and 104a of the flat cables 103 and 104 move in the same direction by a rotation amount smaller than that of the movable housing 101. The flat cables 103 and 104 are in the rewinding state where the winding amount on the outer cylindrical wall of the fixed housing is larger. In events of the winding and rewinding, the rollers 105 and 106 receive forces from the reverse parts 103a and 104a of the flat cables 103 and 104 and move in the same direction.
In the rotary connector using the overlapped flat cables 103 and 104 as the foregoing conventional example, although the first cable 103 is directly wound on the inner cylindrical wall of the movable housing 101, the second flat cable 104 is wound on the outside of the first flat cable 103 which has been wound on the inner cylindrical wall by one turn. Consequently, the diameters of the wound flat cables 103 and 104 on the inner cylindrical wall have the difference corresponding to the thickness of the first flat cable 103. The winding amounts on the inner cylindrical wall or the rewinding amounts from the inner cylindrical wall of the flat cables 103 and 104 are not strictly the same. When the movable housing 101 is rotated, a phenomenon such that the flat cables 103 and 104 are slid and deviated in the winding direction on their contact faces occurs. In this case, since the flat cables 103 and 104 are respectively energized to the outer and inner cylindrical wall sides by reaction forces from the reverse parts 103a and 104a, there is a problem such that the sliding friction when deviation occurs becomes large and is not returned to the original state and the deviated one of the flat cables 103 and 104 is buckled.